Trunking communication systems are known to comprise a plurality of communication units, a limited number of communication resources that are transceived via a predetermined number of repeaters, or base stations, and a communication resource allocator that allocates a limited number of communication resources among the plurality of communication units. The communication resources may comprise a TDM bus, a carrier frequency, a pair of carrier frequencies, and any RF transmission means. Of the communication resources, one is selected as the control channel that transceives operational data between the communication resource allocator and the communication units. The communication units, which may be portable radios and/or mobile radios, are arranged into talk groups by commonality of use. For example, a talk group may comprise communications that are operated by a police department while another talk group comprises communication units operated by a fire department.
Trunking communication systems very efficiently process communications between a large group of communication units. This efficiency is primarily due to the relative large coverage area that one system services and the ability to assign one communication resource to the large group of communication units. Once a communication resource is allocated to the large group, the communication resource allocator periodically transmits a refresher message that indicates which communication resource is assigned to the large group. The refresher message is transmitted on the control channel such that, if any of the communication units in the large group temporarily lose which communication resource is allocated to the large group, it can simply monitor the control channel for the refresher message.
Trunking communication systems also support communications for a relative small group of communication units or even one-to-one communications. However, the system's efficiency is reduced because one communication resource is allocated to a small number of communication units. The efficiency is also reduced because the communication resource allocator continues to periodically transmit refresher messages on the control channel for the small group of communication units. Therefore, a need exists for a method that allows the communication resource allocator to reduce control channel traffic for small groups, or limited audience communications.